7
$\begingroup$

I understand that there were several cases pitot tube failure in a certain way.

The pitot tubes were clogged by ice when the airplane was in cold and wet conditions. The remedy was to exchange the pitot tubes by a different model from a different manufacturer.

As an example, there was an Airworthiness Directive (DGAC 2001-354) applying to the A330 and possibly others, explicitly requiring to replace the model installed when delivered by a specific other model.

The A330 originally came with pitot tubes from Goodrich Sensors and Integrated Systems, part number 0851GR. The Airworthiness Directive of 2001 required to replace these by pitot tubes made by Thales, part number C16195AA, or a specific, more recent model from Goodrich.

I assume all models from all manufacturers have the same basic construction, like all can be heated, for example.

What is it in the construction of the pitot tubes that makes the difference?

Is it just a design flaw in the Goodrich series that was fixed later? Somehow I expect it to be something more general. Are there other manufacturers building pitot tubes with a similar flaw? (That would be a good reason to require replacement with a specific model.)

$\endgroup$
  • $\begingroup$ I'm not entirely clear what you are asking here. $\endgroup$ – Carlo Felicione May 24 '17 at 5:46
  • 1
    $\begingroup$ Your question is almost equivalent to "why some cars are most suseptible to failure than other". There are many design difference and some design choices may be less faulty than other, but there may not be a straight answer for a such wide question. $\endgroup$ – Manu H May 24 '17 at 6:16
  • $\begingroup$ I see your point - I will make it more clear. As an example, there was an Airworthiness Directive applying to the A330 and possibly others, explicitly requiring to replace the model installed when delivered by a specific other model. $\endgroup$ – Volker Siegel May 24 '17 at 6:26
  • $\begingroup$ @VolkerSiegel if you can provide a link to that AD and edit the question for "Why <Model xxx> is susceptible to icing" this question would be much better. $\endgroup$ – kevin May 24 '17 at 7:22
  • $\begingroup$ I'd like to note that the AD you linked to has all Thales C16195AA being replaced by a Goodrich 0851HL and C16195BA parts in positions 1 and 3 being replaced with the same Goodrich pitot tube. I'm trying to find the AD from 2001 you referenced $\endgroup$ – selectstriker2 May 24 '17 at 14:11
1
$\begingroup$

Actually the answer is quite complex, but essentially depends on the local aerodynamics, shape of the probe and the anti-icing power (heating).

Imagine an airplane flying around a cloud, it essentially approaches air with small drops of water floating around, those drops of water impact the pitot tube and some of them keep over the pitot tube surface.

Now, the key question is if that water will or will not become ice. That essentially depends how long the water keeps over the surface and the local temperature.

Keeping on the surface depends on the shape of probe and the local pressure. The water temperature will depend on a balance between the external temperature (also dependent on the local pressure) and the balance of power applied to the probe to avoid freezing.

So, the phenomena is quite complex and depends on all of these factors, and the potential case of pitot tubes prone to icing will likely being a condition unexpected and outside margins as all these factors are taken usually into account.

$\endgroup$
  • $\begingroup$ That's indeed more interesting than I hoped for, thanks! $\endgroup$ – Volker Siegel May 27 '17 at 9:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.